Candidate: Dr. Hansen's goal is to emerge as an excellent independent investigator, concentrating initially on studies of vitamin D metabolism in subjects with rheumatoid arthritis and developing over time multiple interrelated, well-focused and productive clinical research pursuits in bone and mineral metabolism. Receipt of the K23 award will allow Dr. Hansen to complete the University of Wisconsin Clinical Investigator Preparatory Program (CIPP, NIH K30, PI Frank Graziano). The CIPP provides advanced training in the core competencies of patient-oriented research: biostatistics, study design, ethics, scientific writing, presentation and leadership. Environment: The University of Wisconsin is a premier research institution; its Department of Medicine ranks 18th in the country for NIH funding. Dr. Hansen will have access to the Osteoporosis Clinical Research Center, Institute on Aging, and the Biostatistics Department for assistance with her research. Research: Osteoporosis is twice as common in people with rheumatoid arthritis (RA) as non-affected individuals matched for age and gender, leading to two to three-fold higher rates of spine and hip fracture compared to age-matched controls. These osteoporotic fractures are associated with a decline in function and quality of life, and increased medical costs, as is RA itself. An intervention targeting both RA and osteoporosis, which 1) improves bone metabolism, 2 ) elevates functional capacity, and 3) offers immunemodulating benefits would potentially be of great import. Vitamin D is inexpensive, widely available, and likely to offer such benefits. Both hypovitaminosis D and RA cause high bone turnover and subsequent osteoporosis. Existing, albeit limited, data suggest that hypovitaminosis D is common in RA. Thus, it is likely that hypovitaminosis D contributes to osteoporosis in RA. It follows that treatment with vitamin D should reduce bone turnover and improve bone mass. Furthermore, low vitamin D leads to muscle weakness and falls; vitamin D therapy reduces falls by half. Finally, immune-modulating benefits of vitamin D are noted in both animal models of, and humans with, RA. This information provides a compelling rationale for conduct of the proposed study, whereby the prevalence of hypovitaminosis D in RA is estimated, and the deficit is then corrected in half of subjects in a placebo-controlled manner, to document the skeletal, functional and immunologic benefits of vitamin D therapy.